AC Running But Not Cooling? Causes & Fixes for Houston Homes
AC running but not cooling? The 7 most likely causes in Houston homes, what you can safely check yourself, and what each fix costs. Call for same-day help.
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Quick answer: an AC that runs but does not cool almost always comes down to one of seven things: a dirty filter, a dead capacitor or tripped breaker at the outdoor unit, a failed contactor, low refrigerant from a leak, a frozen coil, a failed condenser fan motor, or a worn compressor. The first two you can safely check yourself in five minutes; the rest need a technician with gauges and a meter. If the outdoor unit is silent, call +1 (254) 256-1678 — it is usually electrical and usually fixable the same day.
Check these two things yourself first
- The air filter. A filter clogged solid restricts airflow so severely that the coil can freeze and cooling collapses. Pull it out and hold it to the light — if you cannot see through it, replace it and give the system an hour.
- The outdoor unit. Go outside while the system calls for cooling. Is the condenser fan spinning? Is the unit making any sound at all? A silent outdoor unit with a running indoor blower means the problem is electrical — breaker, disconnect, capacitor or contactor. Also check the breaker panel for a tripped AC breaker, and reset it once only.
Also confirm the thermostat is set to COOL, the setpoint is below room temperature, and the batteries are not dead. These five-minute checks solve a meaningful share of "not cooling" calls.
The likely causes, from common to rare
1. Dirty filter or blocked airflow
The cheapest cause and the most common. Restricted airflow starves the coil, coil temperature drops below freezing, ice builds, and airflow collapses entirely. If you see ice on the lines or the indoor unit, turn the system off and let it thaw completely before restarting with a clean filter.
2. Failed capacitor or contactor
Houston heat kills capacitors faster than almost anywhere in the country. A dead run capacitor leaves the outdoor unit humming or silent while the blower keeps pushing room-temperature air. A burnt contactor does the same by never sending power outside. Both are $100–$400 repairs and the reason "not cooling" is very often a same-day, low-cost fix.
3. Low refrigerant from a leak
Lukewarm air, hissing, ice on the lines, run times that keep getting longer. Refrigerant does not wear out — low charge means a leak, and the repair is find-fix-recharge, not a top-off. Details and per-pound prices on our refrigerant leak repair page.
4. Frozen evaporator coil
Ice on the indoor coil blocks airflow completely. Causes: dirty filter, low refrigerant, or a failing blower. Turn the system off, run the fan-only setting to speed thawing, and find the root cause — just thawing it means it freezes again within days.
5. Failed condenser fan motor
If the outdoor fan is not spinning but the unit hums, the fan motor or its capacitor has failed. The compressor then overheats and shuts down on its internal safety. Turn the system off — running it this way cooks the compressor. See outside AC fan not spinning.
6. Ductwork problems
If some rooms cool and others never do, the system may be fine and the ducts disconnected, crushed or leaking in the attic. A disconnected run in a 140°F Houston attic dumps your cold air where nobody lives. More on duct repair.
7. Compressor failure
The expensive end of the list. A compressor with worn valves pumps weakly; a shorted or locked compressor will not start at all. Before accepting this diagnosis, make sure the capacitor, contactor and windings were actually tested — see compressor repair for what a real diagnosis looks like.
When it is an emergency
In Houston, "not cooling" during a 100°F heat wave with infants, elderly family members or medical needs in the house is a genuine emergency — indoor temperatures climb past 90°F within hours. Call +1 (254) 256-1678 and say so; those calls get prioritized. Also treat it as urgent if you see ice, water leaking, or smell anything burning: those three mean active damage is in progress.
What the fix typically costs
| Cause | Typical Houston range |
|---|---|
| Filter / thermostat (DIY) | $0–$50 |
| Capacitor or contactor | $100–$400 |
| Condenser fan motor | $200–$700 |
| Refrigerant leak find + fix + recharge | $300–$1,000+ |
| Blower motor | $300–$900 (PSC) / $600–$1,500 (ECM) |
| Compressor | $1,300–$2,800 |
Full ranges with sources on the Houston AC repair cost page.
Frequently asked questions
Why is my AC running but not cooling the house?
The most common causes, in order: a dirty air filter restricting airflow, a tripped breaker or dead capacitor stopping the outdoor unit while the indoor blower keeps running, low refrigerant from a leak, a frozen evaporator coil, or a failed compressor. If the outdoor unit is not running at all, the problem is electrical. If both units run but the air is warm, suspect refrigerant or the compressor.
Can low refrigerant cause my AC to run but not cool?
Yes — it is one of the most common causes. Refrigerant does not get used up; if it is low, there is a leak. Signs include lukewarm air, ice on the refrigerant lines, and longer and longer run times. The fix is leak detection, repair and a weighed recharge — not a simple top-off.
Why is my AC blowing warm air after a power outage or storm?
Gulf Coast thunderstorms trip breakers and kill capacitors with power surges. Check the breaker for the outdoor unit first — once. If it trips again immediately, stop resetting it and call: that indicates a hard electrical fault or a shorted compressor, and repeated resets cause real damage.
How much does it cost to fix an AC that runs but does not cool?
It depends entirely on the cause: a capacitor or contactor is $100–$400, a refrigerant leak repair with recharge is $300–$1,000+, a blower motor $300–$900, a compressor $1,300–$2,800. The $75–$200 diagnostic visit identifies which one you are dealing with before you approve anything.
Should I keep running my AC if it is not cooling?
No. If the air is warm, or you see ice anywhere, turn the system off at the thermostat. Running a system low on refrigerant or with a frozen coil can destroy the compressor — turning a few-hundred-dollar repair into the most expensive one on the list.
Need AC repair today?
Call now and we will connect you with a licensed Houston HVAC technician. Exact pricing is confirmed after on-site diagnosis — no surprises.